Reversing motor drive for type bar



y 6, 1969 v. c. MARTIN 3,443,186

REVERSING MOTOR DRIVE FOR TYPE BAR Filed March 28, 1966 Sheet of 10 AMP42 FE/E38 40 AMP BACK CLOCK 44 35 w 53 TB RUN 46 I 32, F T N 0W5 cmcun Rs I I F N ,3

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HUNT CONTROL TB T CONTINUE ACCELERATINC START TIMER TB START TB STOPFEEDBACK F AMP @TO SPEED 35 CLOCK SS STOPPED L 1 s R m l? m 6 L f L mCLam I 0 MW J W mfi CR A M v. c. MARTIN 3,443,186

REVERSING MOTOR DRIVE FOR TYPE BAR May 6, 1969 Sheet Filed March 28,1966 TB DRIVE CK y 1969 v. c. MARTIN REVERSING MOTOR DRIVE FOR TYPE BARFiled Ma'rch 28, 1966 l J QIL |L JL 5 50 5 2 cm GE T 3 s23: .r J. a 52:E5 25 my 255d? M5528 2%; E v ww 5% 2 .aT m wtmo m on 58;: 2 0 0E axw awa ar g 0: 10 m: 2 E J b 2 A z R T T I as $85; 2: mm Tl mm 1 :20 532 N 506 May 6, 1969 v. c. MARTIN 3,443,186

REVERSING MOTOR DRIVE FOR TYPE BAR Filed March 28, 1966 Sheet 6 of 10F16 7 fi NOTTB TR START TmER START L sTART TIMER TIMERF T N f I sTARTsToP cm 2048* RoTsTARTsToP, CLOCK 1024 R TRRcR W I I 155 TB\ OF T NER TBSTART 33 (NOT LINE START) K162 TB STOP; NOT STOP DELAY OR TB STOP UP ToSPEED T TOP T TIMER STOP F T N F T N /IMER I64 Q CLOCK 1024 DELAY CLOCKCLOCK 512 TB STOPPED R R T CLOCK 256 g F J I i F T N NT CYCLE SENSE AMPK E 7 Ts L N L ss i 5 l I 144 I R F 54 36 48 P OR E 90 AccEb A8 5 l uPTo SPEED ss CONT ACCEL I LW Rose. 55 FEEDBACK 55 4 ,RLocTT ss NOT TB REup T m L LL 74 .L R BSTART TIMER, S a -.-s L N T%H%IIE\ L J es W RSV 1 TRUN OR R F T 72 F T STOPPED I (6 TB sToP s N H TUNER TB READY v. c.MARTIN 3,443,186

REVERSING MOTOR DRIVE FOR TYPE BAR Filed March 28, 1966 Sheet 7 of 10 81FIG. 7b

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mm V630 United States Patent Office 3,443,186 Patented May 6, 19693,443,186 REVERSING MOTOR DRIVE FOR TYPE BAR Van C. Martin, Boulder,Colo., assignor to International Business Machines Corporation, Armonk,N.Y., a corporation of New York Filed Mar. 28, 1966, Ser. No. 537,912Int. Cl. H02p 1/22, 1/40, 3/20 US. Cl. 318-257 7 Claims This inventionrelates generally to control system and has reference in particular to areversible drive control system for a motor driving a type bar in a barprinter.

The bar printer is an on-the-fiy front printer in which print hammersdrive flexible type fingers, which are mounted on a horizontally movingtype bar, to impact the ribbon, paper, and platen. The type bar moves inboth directions, and at each end of its travel the type bar is stoppedto await the next print command, at which time it is started up in thereverse direction to print the next line.

The type bar is driven by a motor through a pinion and a rack on one endof the bar. The drive must accelerate the bar rapidly to print velocityand maintain this velocity during printing. At the end of the line itmust rapidly stop the bar. Upon receipt of the next start command itmust accelerate the bar to print velocity in the reverse print directionfor the next line. The requirements of a drive for such an applicationare:

(1) It must be reversible;

(2) It must have sufi'icient torque to accelerate and decelerate thetype bar in a relative short time and displacement;

(3) It must maintain a relatively constant velocity during printing overa wide range of friction loadings and dynamic loadings due to the firingof print hammers; and

(4) It must be reliable and trouble free.

Generally stated, it is an object of this invention to provide forselectively controlling accelerate and decelerate triggers which gatethe drive for a type bar motor in response to clock and feedbacksignals, and for resetting the clock each time a feedback signal occurs,after the lapse of a predetermined start time.

More specifically, it is an object of this invention to initiatevelocity sensing of a print bar drive motor during acceleration, afterthe end of a predetermind start time period, reset a clock provided forcontrolling drive of the motor each time a feedback pulse occurs duringacceleration, and count the elapsed time until the next feedback pulse.

Another object of this invention is to provide in a velocity sensingcontrol for a print bar drive motor, for shutting down the drive circuitin the event that more than a predetermined number of feedback signalsoccur without receiving a clock pulse.

It is also an object of this invention to provide for shutting down thedrive circuit in the event that no feedback pulse is received within apredetermined count of clock pulses while not starting or stopping.

Yet another object of this invention is to provide in an overshootcontrol for a printed circuit motor driving a type bar, for using acounter to produce clock pulses, controlling accelerate and deceleratedrivers by means of clock and feedback pulses from the motor to controloperation of the motor, and for resetting both the accelerate anddecelerate triggers when a feedback pulse occurs before a particularcount is reached by the counter.

It is a further object of this invention to provide for using a binarycounter for not only providing clock pulses to control the operation ofa printed circuit type bar motor, but for also determining the durationof a predetermined start period.

Still another object of this invention is to provide for using clock andfeedback pulses to control opposing drive circuits for a motor driving atype bar, and for deriving a voltage level from an activated one of suchcircuits for preventing activation of the other one of the drivecircuits.

It is also another object of this invention to provide for using aresettable counter driven by a crystal oscillator for producing clockpulses to control operation of a direct current motor, and for resettingthe counter during starting to a count other than zero should a feedbackpulse be detected while the counter is in a predetermined countingrange.

It is also another object of this invention to provide for using abistable device to remember whether the accelerate or decelerate triggerin the control operated or was turned on last, and for providing apredetermined timed pulse in a corrective direction for controllingoperation of the motor should a second successive energization of eithertrigger occur.

According to a preferred embodiment of the invention a printed circuitmotor is reversibly energized to drive a type bar first in one directionand then in the reverse direction in response to successive printcommands. A crystal oscillator driving a multistable binary counterprovides clock pulses for controlling the speed of the motor. Feedbackpulses are provided by a magnetic emitter disc driven by the motor, andare used in conjunction with the clock pulses to control accelerate anddecelerate triggers for applying forward and reverse torque,respectively, for bringing the motor up to speed, maintaining its speedand then stopping the motor at the end of a print line. Duringacceleration the clock is reset to zero, after a predetermined startinterval by each feedback pulse, while the motor is still not up tospeed, and after the motor is up to speed, reset of the clock counter isto a 1 rather than zero, so as to force the clock into the proper phaserelationship, after which the counter runs free to the end of the printline.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings.

In the drawings:

FIGURE 1 is a simplified schematic representation of a type barmechanism and motor controls;

FIGURE 2 is a simplified schematic diagram showing the basic elements ofa type bar motorcontrol according to the prior art;

FIGURE 3 illustrates typical timing curves for the simplified controlcircuit of FIGURE 2;

FIGlUtRES 4a, 4b taken together provide a schematic circuit diagram ofthe type bar drive controls according to the present invention;

FIGURE 5 is a schematic circuit diagram of the clock and overshootinhibit control of the present invention used with the circuit ofFIGURES 4a, 4b;

FIGURE 5a shows typical timing curves for the circuits of FIGURE 5;

FIGURE 6 is a circuit diagram of the printed circuit motor drive circuitfor FIGURE 4b;

FIGURES 7a and 7b taken together provide a schematic circuit diagram ofa modified type bar drive control according to the present invention;

FIGURE 8 is a schematic circuit diagram of a modified clock andovershoot inhibit circuit used with the control circuit of FIGURES 7aand 7b;

FIGURE 8a illustrates typical timing curves of the circuits of FIGURE 8;

FIGURE 9 is a timing diagram illustrating operations during starting andstopping of the printed circuit motor;

FIGURE lO is a schematic representation of an arrangement of a type barflag and solar cells used for producing control signals used in thecircuits of FIGURES 7a, 7b and 8; and

FIGURE 11 is a timing diagram illustrating the operation of the antihuntportion of the control circuits of FIGURES 4a, 4b and 7a, 7b.

Referring particularly to FIGURE 1 of the drawings, a printed circuitmotor PCM is shown connected by means of a pinion 12 to drive a type bar14 having a plurality of flexible type bearing fingers 1 4a, through arack 16 secured to the right end of the type bar. Solar cells 18, 19 and20 with their associated light sources are arranged in conjunction witha flag 22 secured to the type bar for providing Right-Left, TB Stop andLeft-Right signals, respectively, through their associated amplifiers24, 26 and 28 to a block 30 containing the printed circuit motor controlcircuit for aplication to drive circuits 32 controlling operation of themotor PCM. Feedback pulses having a frequency proportional to the speedof the motor are provided by means of a magnetic feedback disc 34 drivenby the motor and an associated pickup 34a through amplifier 36 to thecontrol circuits 30. A type bar signal TB Start is provided from theprinter controls for initiating operations of the motor, as will beexplained hereinafter.

Referring to FIGURE 2 it will be seen that in a prior art simlified formof the control circuit 30, an Accelerate trigger 38 is provided which isset by clock pulses from a clock single shot 40 which is controlled by aclock 42 through an AND circuit 44 in conjunction with a TB Run signal.The trigger 38 is turned on by a set pulse from the single shot 40,which is gated by the off output of a Decelerate trigger 46, asrepresented by the diamondshaped marker. The set input will set thetrigger only if the gate input is turned on prior to the rise of the setsignal. Pulses from the feedback disc 34 are applied through amplifier36 and a feedback single shot 48 to reset the Accelerate trigger 38 andset the Decelerate trigger, when gated by the off output of theAccelerate trigger.

In this simplified control the Accelerate trigger 38 is set on by theclock single shot 40 and turned off by the feedback single shot 48, withits on duration proportional to the phase lag of the feedback signalwith respect to the clock signal. Once a steady state condition isachieved, the drive stays on only long enough to make up losses due tofriction, etc. However, because this is a displacement feedback,velocity can overshoot as shown in FIGURE 3, and continue to oscillate.

When the velocity overshoots, feedback frequency exceeds clock frequencyuntil two feedback pulses occur between consecutive clock pulses, thefirst resetting the Accelerate trigger 38, and the second setting theDecelerate trigger 46 as shown at the point (A) in FIGURE 3. Because thefeedback signal now leads the clock signal in phase, the Deceleratetrigger 46 then continues to come on with successive feedback pulses,being turned off by each clock pulse, until the velocity undershootssufficiently to bring the feedback and clock signals into phase againand two clock pulses occur between the consecutive feedback pulses. TheAccelerate trigger 38 is then set on by the second clock pulse as shownat the point (B) in FIGURE 3. These velocity excursions continue tooccur unless further refinements are employed. Such excursions aresimilar to phase angle variations in a synchronous A-C motor, and areknown as hunting.

Referring to-FIGURES 4a and 4b it will be seen that according to thepresent invention the Accelerate and Decelerate triggers 38 and 46 ofcontrol circuit 30 basically provide the control to the printed circuitmotor drive circuit 32 by L-R and R-L Drive signals through a pair of ORcircuits 50 and 52, whose inputs are supplied by a plurality of ANDcircuits 51-1 through 51-8. Inputs to these AND circuits are providedprimarily from a Start Timer single shot 53 having a duration on theorder of 14 milliseconds in response to the TB Start signal from theprinter controls (not shown), and from a Stop Timer single shot 54having a duration on the order of 16 milliseconds through a Stop Delaysingle shot 56 having a duration on the order of 10 milliseconds andinverter 57. The output of the Start Timer 53 is supplied through aninverter 58 and gated in AND circuit 60 with the inverted output of theStop Timer 54 through inverter 62 to provide a TB Not Start-Stop signal.The direct output of the Start Timer 53 provides TB Start Timer signal.The output of Stop Timer single shot 54 provides a TB Stop Timer signal.A Decelerate signal is provided to the AND circuits 51-4 and 51-5 fromthe on output of the Decelerate trigger 46 through OR circuit 64 whilean Accelerate signal is provided to AND circuits 51-5 and 51-8 throughOR circuit 66 from the on output of the Accelerate trigger 38. ALeft-to-Right signal (L-R) is provided to AND circuits 51-1, 51-2, 51-5and 51-6 from a L-R latch 68, while a Right-to-Left signal (R-L) isprovided to AEND circuits 5-1-3, 51-4, and 51-7, 51-8 by a R-L latch 70.The latch 68 is turned on by the on output of a Type Bar Run latch 72through A NID circuit 74 in conjunction with L-R gate signal from solarcell 20, while a latch 70 is turned on through a corresponding ANDcircuit 76 by TB Run in conjunction with a R-L gate signal from solarcell 18. AND circuit 69 provides a TB Stopped signal from the offoutputs of latches 68 and 70 A hunt control circuit 80 utilizing anIncrease Speed single shot 82 and a Reduce Speed single shot 84 forsupplying predetermined duration signals through OR circuits 64 and 66to the PCM drive circuit 32 through AND circuits 51-1 through 51-8, isutilized in accordance with the present invention to minimize theamplitude of velocity excursions as the drive switches betweenaccelerate and decelerate modes. The single shot 82 having a duration onthe order of 350 microseconds is turned on by a Too-Slow trigger 86,while the single shot 84 having a duration on the order of 200microseconds is turned on by a Too-Fast trigger 88. These triggers arecontrolled by a Hunt Cycle Sense latch 90, which is set and reset by theon outputs of the Decelerate and Accelerate triggers 46 and 38,respectively. The latch provides gate signals to the latches 86 and 88,the set signals therefor coming from the on outputs of the Accelerateand Decelerate triggers themselves. FIG. 11 shows timing curvesillustrating the operating mode of the hunt control.

In order to check against type bar jam, feedback or amplifier failure,clock failure, or failure of either the Accelerate or Deceleratetriggers to reset, a checking circuit is provided in this embodiment ofthe present invention. This circuit comprises a two-stage binary counterof triggers 101 and 102, which counts clock pulses and feedback pulsesfrom OR circuit 104, with reset of the triggers being provided throughinverter from an OR circuit 106 having as inputs L-R Drive signal andR-L Drive signal. OR 106 also supplies gate signals to trigger 101through AND circuits 108 and 108 through AND circuit 112 in conjunctionwith the Not Start-Stop signal. Accordingly, when both the L-R and R-Ldrives are off (which should be once every clock cycle when not startingor stopping) the counter is reset. If the counter ever reaches a countof 3, a Type Bar Check latch 114 is set through AND circuit 116, and theoutput is used to reset the Type Bar Run latch 72 to remove drive fromthe motor.

Referring to FIGURE 5 it will be seen that according to the presentinvention, a clock single shot 42b producing clock pulses is driven by afive-stage multistable binary counter utilizing bistable trigger devicesT1, T2, T4, T8 and T16. The counter is driven by a crystal oscillator42a through AND circuit 117. Reset of the counter to zero is effectedthrough OR circuit 118 which resets triggers T2, T4, T8 and T16 inresponse to an output from a Not Up-to-Speed single shot 132, or anUp-to- Speed single shot 120 which calls for the clock to be reset to a1 rather than to a Zero, the output of a single shot 120 being appliedto set the trigger T1. The Up-to-Speed single shot 12!} is activated bythe on output of an Up-to- Speed latch 122, which during the TB Starttimer period is held reset through OR circuit 124, and is set when thetype bar comes up to speed, through AND circuit 126. Feedback pulses areapplied thereto from AND circuit 128 while the 16-stage of the counteris on and TB Start timer is off, as evidenced by the output of the ANDcircuit 130 having an input connected to the output of the trigger T16,and another connected through inverter 131 to the TB Start timer. ANDcircuit 129 is used to provide a Continue Accelerating signal forresetting the Accelerate trigger 38 by combining the off output of theUp-to- Speed latch 122 with the output of counter trigger T2.

During acceleration and before the motor reaches speed, the clocktriggers are reset through OR circuit 118 from a. Not Up-to-Speed singleshot 132 which is turned on by AND circuit 134 in response to theinverted output of the trigger 16 through inverter 136, a feedback pulsefrom AND 128, and the off output of the Not Up-to-Speed latch 122. Theoutput of the single shot 132 not only resets the triggers T2, T4, T8and T16 through OR circuit 118 but also resets T1 over conductor 138 soas to reset the counter to zero.

In operation, Accelerate trigger 38 is turned on by pulses from clocksingle shot 42b and turned off by pulses from feedback single shot 48,but during starting, PCM drive circuit 32 is energized through AND 51-2in response to TB Start timer L-R and Not TB Check. The Start Timersingle shot 52 provides continuous acceleration drive for 14milliseconds, or until the motor is approximately up to speed. StartTimer single shot 53 is fired by the TB Start signal from the printercontrols through AND 73 and in turn sets the TB Run latch 72 and eitherthe Left-to-Right or the Right-to-Left latch 68 or 70, depending uponthe type bar position as evidenced by the LR gate or R-L gate signalsfrom solar cells 20 and 18 through AND circuits 74 and 7-6,respectively. When the motor is up to speed, the Accelerate andDecelerate triggers 38 and 46 take over as previously described, andacceleration is continued for example, through AND 51-1 in response toAccelerate (from OR 66), L-R, Not TB Start-Stop, and Not TB Check. Whenthe TB Stop solar cell 19 is sensed, the Stop Delay single shot 56fires, providing sufiicient type bar displacement before stopping sothat when the type bar starts up in the reverse direction it will beup-to-speed before reaching the first position. At the end of the StopDelay signal, the Stop Timer single shot 54 provides deceleration drivethrough AND 51-6 and OR 52, or AND 51-3 and OR 50 of such duration as tobring the type bar to a stop, the direction of the voltage applied tothe motor being a function of the type bar direction.

As shown in FIGURE 5', high frequency output of crystal oscillator 42ais stepped down through a fivestage binary counter whose last step is ofthe frequency desired. The five-stage counter permits the clock outputphase to be shifted to within /32 of a cycle of any phase by resettingthe counter to the proper count. Velocity sensing during acceleration,but after the termination of Start Timer signal, is achieved byresetting the clock through the Not Up-to-Speed single shot 132 eachtime a feedback pulse occurs, and counting the elapsed time before thenext feedback pulse. The Start Timer single shot 52 is set to turn offafter the velocity has reached approximately of ideal velocity. Duringthe Start Timer signal, velocity sensing is ineffective because theUp-to-Speed latch 122 is held reset by TB Start signal through OR 124.Thereafter should a feedback pulse occur before the count of 32, asdetermined by the 16-stage of the counter being on (the counter havingbeen reset to zero by the previous reset pulse), and the oscillatoroutput is down as evidenced by the inverted signal from inverter 140,the

6 Up-to-Speed latch 122 is set, firing the Up-to-Speed single shot 120.The counter is thereupon reset to 1 to establish the proper phaserelationship, and both the Accelerate and Decelerate triggers 38 and 46are reset through OR circuits 142 and 144 respectively. The clock thenruns free through the end of the line and overshoots are controlled to apermissible value.

Any tendency of the system to oscillate or hunt is mimmized according tothe present invention, by the Hunt Control circuit 80, wherein the HuntCycle Sense latch senses the transition between acceleration anddeceleration mode. At this time a proper duration drive pulse fromeither the Increase Speed single shot 82 or the Reduce Speed single shot84 is applied to the motor through OR 66 or OR 64 so that the velocitycan be corrected to maintain a minimum placement error. The Too-Fast andToo- Slow triggers 86 and 88 switch only after two successivedeceleration or acceleration operations, respectively, thus reducingdisturbances caused by erroneous feedback. The Too-Fast trigger -88fires the Reduced Speed single shot 84, and the Too-Slow trigger 86fires the Increase Speed single shot 82. Outputs from these single shotsare applied to the drive circuit 32 through OR circuits 64 and 66 andAND circuits 511 and 518, 51-4 and 51-5, respectively, as shown by thetiming curves of FIGURE 11.

When hunting occurs, a maximum velocity error is present at the timethere is zero displacement error. The hunt control single shots fireonly upon the transition from accelerate mode to decelerate mode or viceversa (the transition indicating zero displacement error) and compensatefor the velocity error which exists at that time. The single shots maybe though of as providing coarse correction at the point of transition,with the normal feedback pulses which are of much shorter durationproviding the fine correction.

Referring to FIGURE 6 it will be seen that the printed circuit motordrive circuit 32 may comprise a bridge circuit of power transistors T1,T2, T3, T4, connected to effect energization in the armature PCMA of themotor in opposite directions in response to LR and R-L drive signals.The L-R drive signal is used to control transistors T1 and T3,transistor T9 being connected to turn on in response to a negative-goingL-R drive signal and driving the base of transistor T7 sufficientlynegative to turn it on, which causes the base of transistor T5 to becomepositive. Transistor T5 turning on renders the base drive of thetransistors T1 and T3 sufficiently negative to turn them on and effectL-R operation of the motor. Transistor T10, through transistors T8 andT6, likewise controls the base drive of the transistors T2 and T4 foreffecting energization of the printed circuit motor armature in responseto a R-L drive signal. Diodes D1 and D2 connect the bases of transistorsT9 and T10 to the collectors of transistors T6 and T5, respectively. Asis evident from FIGURE 6, if transistors T1, T2, T3 and T4 were allsimultaneously in an on state, two short circuits from ground to thenegative terminal of the source would exist, one through transistors T1and T4, and the other through T2 and T3. Accordingly if transistor T5 isturned on to energize drive transistors T1 and T3, the base oftransistor T10 will be clamped through diode D2 so as to prevent turn onof transistor T10 to attempt opposite energization of the printedcircuit motor armature at the same time.

Referring to FIGURE 8 it will be seen that in another embodiment of thepresent invention, the clock has been modified to provide a six-stagebinary counter for providing clock pulses from oscillator 42a throughthe clock single shot 42b, so as to divide the clock cycle into 64 equalparts, thus permitting the clock output phase to be switched to of acycle of any phase desired by resetting the counter to the proper count.Reset of the clock is substantially identical to that described inconnection with the operation of the clock in FIGURE 5, the Not Up-to-Speed single shot 122 being triggered through AND circuit 128' inresponse to the 32 trigger and Not 64 trigger outputs. Instead ofutilizing the Start Timer and Stop Timer single shots 52 and 54 ofFIGURE 4a, six additional stages have been added to the binary counterin order to provide timed outputs for effecting the functions of thesesingle shots. Since the counter will be used to provide the Start Timersignal in the circuit of FIGURES 7a, 7b, and Up-to-Speed gate latch 150is provided for furnishing an input to AND circuit 126 for setting theUp-to-Speed latch 122 for preventing setting of this latch before thecounter is reset following the Start Timer signal. The latch 150 turnson the AND circuit 152, which gates Not TB Start Timer with the outputof the Not Upto-Speed single shot 132. Reset of latch 122 is through OR124'.

Referring now to FIGURES 7a and 7b it will be seen that the gatingcircuits or AND circuits 51-1 through 51-8 for providing the LR and R-Ldrive signals to the printed circuit motor drive circuit 32 aresubstantially the same as in FIGURES 4a and 4b and operation of thecontrol circuits is substantially the same as described in connectiontherewith. Instead of using a single shot 52 to provide the Start Timersignal, a Start Timer trigger 154 is employed, which is turned onthrough AND 155 by TB Start and TB Stopped from AND 69, and is turned01f at a count of 3072 by a gate signal from the counter 2048 triggerand a set signal from the counter 1024 trigger to give a start time ofapproximately 12 milliseconds. The Stop Timer single shot 54 is replacedby a Stop Timer trigger 156 which is turned on through AND circuit 158which gates the on output of a Stop Delay trigger 160 with the clocksignals 1024 and 512. The clock signal 256 is used as a set signal sothat the Stop Timer turns on at a count of 1792 and is turned off by theclock signal Not 2048 (clock trigger 2048 Off signal) so that it turnsoff at a count of 4096. An adjustable TB Stop Tuner single shot 162connected to the off output of the Stop Timer extends the count for upto 2 milliseconds providing its output through OR circuit 164, so thatthe duration of deceleration provided by the Stop Timer and Stop Tunermay be adjusted to bring the type bar exactly to a halt.

The checking circuit 166 is also basically the same as the checkingcircuit 100 of FIGURE 4b, but has an additional stage, so as to providefor turning on the Type Bar Check latch 114 if the counter ever reachesa count of six. The counter is driven through OR circuit 104 in responseto clock and feedback pulses, and is set through inverter 110 inresponse to the absence of either L-R or R-L signals from OR circuit106. OR circuit 170 is provided for setting the check latch 114 inresponse to a Not TB Recognition Signal, which is derived from, andoccurs when all of the type bar photocells are exposed; at a time whenthe TB Run signal is on, through AND circuit 172; when the type 'bar isnot up-to-speed and Line Start or Print Gate is on, through AND circuit174; or when the Start-Stop signal occurs with Line Start through ANDcircuit 176.

Referring to FIGURE there is a schematic representation of anarrangement of solar cells 180, 181 and 182 which are used in connectionwith a flag having stepped portions 183 and 184 for producing theDirection, Line Start, and Ready signals used in the circuitry ofFIGURES 7a and 7b.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. A control circuit for a direct current motor comprising:

a clock having an oscillator driving a multistage counter of bistabledevices to produce clock pulses,

a source of feedback pulses having a rate dependent on the motor speed,

circuit means including a first bistable device having on and olf statesoperative to connnect the motor to a source of electrical energy todevelop forward torque in the motor in the on state,

circuit means including a second bistable device having on and offstates operative to connect the motor to a source of electrical energyto develop reverse torque in said motor in the on state,

means connecting the speed dependent pulse source to said first bistabledevice to switch said first device to the off state,

other means connecting the speed dependent pulse source to themultistage counter selectively operable to reset the bistable devices ofsaid counter to different values,

means connecting the counter to said second bistable device operative toswitch said second device to the off state,

circuit means interconnecting the first and second bistable devices andrespectively connecting the first and second bistable devices to thecounter and to the source of feedback pulses operative to switch thefirst and second bistable devices to the on state.

2. A control system as defined in claim 1 characterized by:

means including a single shot connected to provide a predetermined timedconnection of the motor to the source to produce a torque in onedirection to change the speed of the motor,

and means connecting said first bistable device and said single shot forrendering said first bistable device ineffective during saidpredetermined timed connection of the motor by said single shot.

3. A control system as defined in claim 1 characterized by:

a single shot connected to provide a predetermined timed connection ofthe motor to develop a torque in the forward direction substantiallygreater than the minimum duration provided by said first bistabledevice,

a hunt cycle sense latch connected to the first and second devices to beswitched on and off with switching of said devices,

a trigger connected to the single shot and connected to be controlled'by both the first bistable device and the hunt cycle sense latch toturn the single shot on only with a second consecutive switching on ofsaid first bistable device and connect the motor to develop forwardtorque for a time greater than the minimum duration of the forwardtorque provided by the first bistable device.

4. A control system as defined in claim 1 characterized by:

timer means for producing a start timer signal of predetermined durationafter receipt of a start signal,

an additional bistable device connected to reset the counter to a onecount,

and means including an AND connecting the additional bistable device tothe source of feedback pulses, the counter and the timer means to effectoperation thereof in response to a feedback pulse occurring during apredetermined count of the counter, but after the termination of thetimer signal.

5. A control system as defined in claim 1 characterized by: w

an additional bistable device connected to reset the counter to a onecount,

another bistable device connected to be turned oif by the counter at apredetermined count to provide a signal of predetermined durationfollowing a start signal,

and circuit means connecting said additional bistable device to saidanother bistable device, said counter and said source of feedback pulsesto effect operation of said additional bistable device in response to afeedback pulse occurring during a predetermined count after the anotherbistable device is turned off. 6. A control system as defined in claim 1characterized by:

the other means connecting the speed dependent pulse source to themultistage counter is so connected as to reset the counter to zero, andsaid other means is so connected to the another bistable device as to berendered ineffective for a predetermined time after a start signal isreceived. 7. A control system as defined in claim 4 characterized by:

an up-to-speed bistable device which has on and 01f states and isconnected to the source of feedback 15 pulses and the counter to beturned on by a speed dependent pulse occurring while a predeterminedstage of the counter is on,

said up-to-speed bistable device being connected to said anotherbistable device so as to be held reset by said another bistable deviceproviding the signal of predetermined duration following a start signal,and being connected to said multistage counter to reset it to a onecount.

References Cited UNITED STATES PATENTS 3,154,730 10/1964 Houldin 3183183,192,461 6/1965 Hohne 318-318 3,281,635 10/1966 Hohne 3l8318 3,348,10710/1967 Hamby 318318 ORIS L. RADER, Primary Examiner.

K. L. CROSSON, Assistant Examiner.

U. S. Cl. X.R. 3l8-265, 282, 318

1. A CONTROL CIRCUIT FOR A DIRECT CURRENT MOTOR COMPRISING: A CLOCKHAVING AN OSCILLATOR DRIVING A MULTISTAGE COUNTER OF BISTABLE DEVICES TOPRODUCE CLOSK PULSES, A SOURCE OF FEEDBACK PULSES HAVING A RATEDEPENDENT ON THE MOTOR SPEED, CIRCUIT MEANS INCLUDING A FIRST BISTABLEDEVICE HAVING ON AND OFF STATES OPERATIVE TO CONNECT THE MOTOR TO ASOURCE OF ELECTRICAL ENERGY TO DEVELOP FORWARD TORQUE IN THE MOTOR INTHE ON STATE, CIRCUIT MEANS INCLUDING A SECOND BISTABLE DEVICE HAVING ONAND OFF STATES OPERATIVE TO CONNECT THE MOTOR TO A SOURCE OF ELECTRICALENERGY TO DEVELOP REVERSE TORQUE IN SAID MOTOR IN THE ONE STATE, MEANSCONNECTING THE SPEED DEPENDENT PULSE SOURCE TO SAID FIRST BISTABLEDEVICE TO SWITCH SAID FIRST DEVICE TO THE OFF STATE, OTHER MEANSCONNECTING THE SPEED DEPENDENT PULSE SOURCE TO THE MULTISTAGE COUNTERSELECTIVELY OPERABLE TO RESET THE BISTABLE DEVICES OF SAID COUNTER TODIFFERENT VALUES, MEANS CONNECTING THE COUNTER TO SAID SECOND BISTABLEDEVICE OPERATIVE TO SWITCH SAID SECOND DEVICE TO THE OFF STATE, CIRCUITMEANS INTERCONNECTING THE FIRST AND SECOND BISTABLE DEVICES ANDRESPECTIVELY CONNECTING THE FIRST AND SECOND BISTABLE DEVICES TO THECOUNTER AND TO THE SOURCE OF FEEDBACK PULSES OPERATIVE TO SWITCH THEFIRST AND SECOND BISTABLE DEVICES TO THE ON STATE.